Question

Glycogen synthase a is activated by ___________

(a) Phosphorylation catalyzed by GSK3

(b) Dephosphorylation catalyzed by GSK3

(c) Phosphorylation catalyzed by pyruvate kinase

(d) Phosphorylation catalyzed by pyruvate carboxylase

This question was addressed to me during an internship interview.

This key question is from Coordinated Regulation of Glycogen Synthesis and Breakdown in division Principles of Metabolic Regulation: Glucose and Glycogen of Biochemistry

Answer 1

The correct answer is (a) Phosphorylation catalyzed by GSK3

Best explanation: A protein kinase (PDK-1) that is activated when bound to PIP3 activates a second protein kinase (PKB) which phosphorylates glycogen synthase kinase 3 (GSK-3). The inactivation of GSK3 allows PP1 to dephosphorylate glycogen synthase converting it to its active form.